Properties of Water- Cohesion and Adhesion: Videos & Practice Problems
Properties of Water- Cohesion and Adhesion center on how water molecules interact through hydrogen bonding. Cohesion means water sticking to water, while adhesion means water sticking to other substances. Because water is polar, it can form hydrogen bonds with nearby water molecules and with other polar or charged materials, such as glass. These interactions explain why water behaves differently from many other liquids.
Together, cohesion and adhesion give water a relatively high surface tension, which is the difficulty of breaking the surface of a liquid with force. In water, cohesive forces occur when the hydrogen atoms of one H2O molecule hydrogen bond to the oxygen atoms of adjacent H2O molecules. This strong intermolecular attraction helps the water surface resist disruption and allows the surface to act almost like a thin film under gentle conditions.
Properties of Water- Cohesion and Adhesion
Properties of Water- Cohesion and Adhesion Example 1
Which of the following effects can occur because of the high surface tension of water?
a) Lakes cannot freeze solid in winter even with extremely low temperatures.
b) A spider can walk across the surface of a small pond.
c) Organisms can resist temperature changes, although they give off heat due to chemical reactions.
d) Sweat can evaporate from the skin, helping to keep people from overheating.
Cohesive forces in liquid water occur when:
a) The H atoms on molecules of H2O hydrogen bond to O atoms on adjacent molecules of H2O.
b) The H atoms on molecules of H2O hydrogen bond to other H atoms on adjacent molecules of H2O.
c) The atoms on molecules of H2O hydrogen bond to other O atoms on adjacent molecules of H2O.
d) None of the above are correct.
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Cohesion in water refers to the attraction between water molecules themselves, causing them to stick together. This happens because water molecules form hydrogen bonds with each other, where the hydrogen atom of one molecule bonds to the oxygen atom of a neighboring molecule. Adhesion, on the other hand, is the ability of water molecules to stick to other substances that are not water, such as glass or other polar or charged surfaces. Both cohesion and adhesion are important because they contribute to water's unique properties, including its high surface tension, which allows water to resist external force and support small objects on its surface.
Hydrogen bonding is the key force behind both cohesion and adhesion in water. In cohesion, hydrogen bonds form between water molecules, specifically between the hydrogen atom of one molecule and the oxygen atom of another, creating a strong attraction that holds the molecules together. For adhesion, water molecules form hydrogen bonds with other polar or charged substances, such as glass. This ability to hydrogen bond with both water molecules and other materials explains why water can stick to itself and to different surfaces, leading to important phenomena like surface tension and capillary action.
Water has a high surface tension because of the strong cohesive forces between its molecules, which are due to extensive hydrogen bonding. These hydrogen bonds create a network of attractions that make it difficult to break the surface of water. This high surface tension allows water to resist external forces and supports small objects, like a paper clip, on its surface without sinking. Most other liquids do not have such strong hydrogen bonding, so their surface tension is much lower. This property is biologically important because it helps water act as a solvent and supports various life processes.
Cohesion and adhesion are critical for water's function as a solvent in biological systems. Cohesion keeps water molecules together, maintaining the liquid state and allowing it to flow smoothly. Adhesion enables water to interact with and dissolve various polar and charged substances, such as salts and sugars, by forming hydrogen bonds with them. This interaction helps transport nutrients and waste in organisms. Together, these properties allow water to dissolve many substances essential for life, facilitating biochemical reactions and maintaining cellular functions.
Water's polarity means it has a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This polarity allows water molecules to form hydrogen bonds not only with each other but also with other polar or charged surfaces, such as glass. Glass is polar, so water molecules adhere to it by forming hydrogen bonds with the glass surface. This adhesion helps water climb up surfaces in processes like capillary action and contributes to water's ability to wet surfaces, which is important in many biological and environmental contexts.
